Optimal hydrogen storage in sodium substituted lithium fullerides

A relevant improvement in the hydrogen storage capability of lithium fullerides is obtained by the co-intercalation of a small amount of sodium

Fundamentals of hydrogen storage in nanoporous materials

Physisorption of hydrogen in nanoporous materials offers an efficient and competitive alternative for hydrogen storage. At low temperatures (e.g. 77 K) and moderate pressures (below 100 bar) molecular H2 adsorbs reversibly, with very fast kinetics, at high density on the inner surfaces of materials such as zeolites, activated carbons and metal–organic frameworks (MOFs). This review, by experts of Task 40 ‘Energy Storage and Conversion based on Hydrogen’ of the Hydrogen Technology Collaboration Programme of the International Energy Agency, covers the fundamentals of H2 adsorption in nanoporous materials and assessment of their storage performance. The discussion includes recent work on H2 adsorption at both low temperature and high pressure, new findings on the assessment of the hydrogen storage performance of materials, the correlation of volumetric and gravimetric H2 storage capacities, usable capacity, and optimum operating temperature. The application of neutron scattering as an ideal tool for characterising H2 adsorption is summarised and state-of-the-art computational methods, such as machine learning, are considered for the discovery of new MOFs for H2 storage applications, as well as the modelling of flexible porous networks for optimised H2 delivery. The discussion focuses moreover on additional important issues, such as sustainable materials synthesis and improved reproducibility of experimental H2 adsorption isotherm data by interlaboratory exercises and reference materials

Addition of transition metals to lithium intercalated fullerides enhances hydrogen storage properties

We report an innovative synthetic strategy based on the solid state reaction of fullerene C60 with lithium-transition metals alloys (platinum and palladium), which provides transition metal-decorated lithium intercalated fullerides, with improved hydrogen storage properties. Compounds with Li6Pt0.11C60 and Li6Pd0.07C60 stoichiometry were obtained and investigated with manometric/calorimetric techniques which showed an 18% increase of the final H2 absorbed amount with respect to pure Li6C60 (5.9 wt% H2) and an improved absorption process kinetic. The absorption mechanism was investigated with X-rays diffraction which allowed to identify the formation of the hydrofullerides. Scanning Electron Microscopy was applied to gain information on transition metal distribution and detected the presence of platinum and palladium aggregates which are shown to perform a surface catalytic activity towards hydrogen molecule dissociation process

Molecular Rotors in a Metal–Organic Framework: Muons on a Hyper-Fast Carousel

Using muon-spin spectroscopy, we study the exceptional dynamical properties of rotating molecular struts engineered within a Zn-based metal–organic framework at cryogenic temperatures, where the internal motions of almost any other organic substance are quenched. Muon-spin spectroscopy is particularly suited for this aim, as the experimental evidence suggests several implantation sites for the muons, among which at least one directly onto the rotating moiety. The dynamics of the molecular rotors are characterized by the exceptionally low activation energy EA ∼ 30 cal mol–1. At the same time, we evidence a highly unusual temperature dependence of the dipolar interaction of muons with nuclear magnetic moments on the rotors, suggesting a complex influence of the rotations on the muon implantation and diffusion

In Situ Neutron Powder Diffraction of Li<inf>6</inf>C<inf>60</inf> for Hydrogen Storage

Li6C60 is the best performing fullerene-derived hydrogen storage material. We report the thermal evolution of Li6C60 upon deuterium absorption up to 330 °C and under 60 bar D2 using in situ neutron powder diffraction. We are able to discern between the hydrogenation of Li6C60 and the segregation of lithium hydride (LiD) during absorption from a mechanistic point of view. During absorption, Li6C60 undergoes several phase transitions, involving the partial segregation of Li in form of hydride and the expansion of the fcc lattice followed by a bcc rearrangement of the deuterated fullerenes. The amount of absorbed deuterium was determined by the analysis of the variation in the scattered neutron intensity and confirmed by a desorption measurement

Effect of Ni-nanoparticles decoration on graphene to enable high capacity sodium-ion battery negative electrodes

Modification of graphene has been undertaken in many research contexts in order to improve its properties. In this study, we examine Ni-nanoparticles decoration on graphene and its effect on sodium-ion battery performance. A definite trend is observed on the relationship between Ni-nanoparticles concentration (and hence size) and battery performance. Comparable capacities on the order of 420 mAhgâ\u88\u921 after 20 cycles at 100 mAgâ\u88\u921 is observed for the 3 relatively high Ni-concentration samples NiC10, NiC40, and NiC80. As the Ni:C ratio decreases, a decreasing trend is observed in the measured capacity, with NiC200, NiC500, and NiC1000 producing capacities of 350 mAhgâ\u88\u921, 380 mAhgâ\u88\u921, and 300 mAhgâ\u88\u921 respectively after 20 cycles at the same rate. Ex situ energy dispersive X-ray spectroscopy, scanning, and transmission electron microscopy shows the morphology of the Ni-nanoparticles decorated graphene and assists in quantifing their sodium content, emphasizing the increasing sodium content with increasing Ni-nanoparticles concentration. This systematic study details how Ni-nanoparticles concentration on graphene surfaces can be manipulated to enhance electrochemical performance, and that higher concentrations up to NiC10 favour better performance. For a compromise between performance and cost (Ni cost), the best composition is NiC500 which favors best performance with the least Ni decoration

Superconducting Fluctuations Observed Far above T_{c} in the Isotropic Superconductor K_{3}C_{60}

Alkali-doped fullerides are strongly correlated organic superconductors that exhibit high transition temperatures, exceptionally large critical magnetic fields, and a number of other unusual properties. The proximity to a Mott insulating phase is thought to be a crucial ingredient of the underlying physics and may also affect precursors of superconductivity in the normal state above T_{c}. We report on the observation of a sizable magneto-thermoelectric (Nernst) effect in the normal state of K_{3}C_{60}, which displays the characteristics of superconducting fluctuations. This nonquasiparticle Nernst effect emerges from an ordinary quasiparticle background below a temperature of 80 K, far above T_{c}=20  K. At the lowest fields and close to T_{c}, the scaling of the effect is captured by a model based on Gaussian fluctuations. The behavior at higher magnetic fields displays a symmetry between the magnetic length and the correlation length of the system. The temperature up to which we observe fluctuations is exceptionally high for a three-dimensional isotropic system, where fluctuation effects are expected to be suppressed